This is a review of the paper, "Use of Optimization Models in Public Sector Planning" by E. Downey Brill, Jr. published in Management Science, INFORMS in May, 1979.
The author discusses the use of multi-objective optimization methods in solving real time public sector planning. He is positive about the use of the optimization methods but in a limited perspective as most of the models in lieu of simplicity have a tendency to curtail some of the important decision elements which generally make the model complex. He also mentions that the use of trade-off curves and pareto fronts is limited as the exclusion of some important factors or an oversimplification may result the optimal solution to lie in the sub-optimal or inferior alternatives region than on the frontier of the so obtained trade-off curves. He also proposes the use of optimization schemes as tools in the planning process which is much more comprehensive and takes into account many factors which are not easily modelled.
Thoughts?
I completely agree with the author in the case of the scope of the use of optimization as tools in a comprehensive planning process with limited use. I also understand the fact that with advanced methods being developed optimization might have a fair chunk of a rational planning process the recent failures involving complex social models used in the optimization process may still allow us to think before we act.
Wednesday, April 29, 2009
Assignment-10 a
This is a review of the paper "GA-QP Model to Optimize Sewer Systems Design" by T.C.Pan et.al. published in the Journal of Environmental Engineering (ASCE), January 2009.
In this paper the authors have discussed using a hybrid optimization scheme to come up with the best cost sewer systems design. A genetic algorithm approach is proposed to find low cost schemes for sewer systems where the costs are calculated through a quadratic programming approach which takes care of pipe geometry, topological and other deterministic factors to come up with the cost of a candidate scheme. The candidate schemes thus obtained are represented as chromosomes and the fitness function being the reciprocal of the total cost of the scheme represented. The genetic algorithm uses three operations of selection, crossover, and mutation with the selection probability being proportional to the fitness of the individual chromosome.
The authors propose that the QP-GA approach could yield better results than a LP-GA approach used previously by Berry et.al. and others to simplify non-linear problems as QP conserves some non-linearty while exihibiting a uni-modal behavior facilitating a global optimal solution. Though with the use of the GA its still not guaranteed.
The authors also raise concerns over the factors like human intervention etc which aren't easily modelled and not included in this approach. They in turn use the idea of Modeling to generate alternatives(MGAs) as an approach to come up with new and different solutions to get near-optimal solutions. Finally, they do some comparative studies of the new QP-GA solutions and other classical methods like the DDDP (Discrete Dynamic Programming) etc.
Thoughts:
I like the idea of the hybrid optimization and alternative solutions but I would really like to see a way to establish hydraulic feasibility of such schemes. Like coupling this system to a hydraulic modeling s/w like sewerCAD and see for hydraulic instabilites and feasibilites in terms of O&M.
Wednesday, April 15, 2009
Assignment-9
This is the review of the paper titled "Compromise Programming Methodology for Determining Instream Flow under Multi-objective Water Allocation Criteria" by Jeng-Tzong Shiau and Fu-Chun Wu, in the Journal of the American Water Resources Association in October, 2006.
This paper is about implementing a quantitative assessment framework for determining the instream flow under multi-objective water allocation criteria using a the Range of Variability Approach (RVA) to evaluate hydrologic alterations caused by flow diversions. The resulting degrees of alterations for the 32 Indicators of Hydrologic Alterations (IHAs) are integrated into one overall degree of Hydrologic Alteration. The inclusion of this index in the objective function to optimize a water allocation scheme to minimize hydrologic alterations and water supply shortages using compromise programming is suggested.
The proposed methodology is applied to a case study of the Kaoping diversion weir in Taiwan that is designed to simultaneously assure the water supply reliability and sustain natural flow variability. The Kaoping Creek in southwestern Tainwan is 171 km long and has the largest drainage area(3,257 km2) on the island, the average annual runoff being about 8.5 billion m3. The creek supplies major proportions of the total water demand in this region. The Kaoping diversion weir with a design diversion capacity of 35 m3/s was completed in 1999, built to supply for the increasing municipal demands. The Kaoping Creek provides habitats for some endemic species and it is believed that agricultural withdrawals and municipal diversions both can effect the aquatic biota considerably dowstream of the Kaoping weir. Currently a minimum instream flow of 9.5 m3/s is being released at the weir but a minimum flow is unable to provide sufficient flow variation which is recognosed as a primary driving force for sustaining the integrity of aquatic ecosystems.
In RVA analysis, a range of variation for each IHA is determined from the prediversion flows. In this study the target range for each IHA was bracketed between 25th and 75th percentile values as suggested by Richter et al. (1998). The weir operations are aimed to make post diversion flow conditions reach the established RVA ranges at the same frequency as that of the prediversion flows.
This is a multi-objective decision making problem which involves the minimizing of the hydrologic impacts and water supply shortages as the operational goals for the Kaoping weir. The objective function can be expressed as a function of shortage ratio of the registered agriculural withdrawals, shortage ratio of the projected diversion for municipal supplies and the combined index for Hydrological Alterations whose definitions are provided in the article. All these can be expressed as the function of the instream flow value as decision variable.
The compromise programming algorithm is adopted as the authors believe its suited for the discrete problem and is still felixible for the preferences of the decision makers concerning the relative importance of each goal considered. Compromise programming identifies the optimal solution as the one that has the shortest distance to an ideal point where the multiple objectives simulatneously reach their minimum values. The ideal point is practically inachievable but may be used as a base point.The objective function involves the use of the base point and the worst point wrt each goal. It also involves the use of weights in order to decide the preferred goals.
The results indicate that the current realease of 9.5 m3/s as a minimum instream flow does not effectively restore the natural flow variations. Increasing the amount of instream flow release would reduce the overall degree of hydrologic alteration; however, this is achieved at the cost of increasing the water supply shortage ratios. An equal weighting to both water supply reliability and natural flow variability would suggest a minimum flow of 26 m3/s which is supported by the authors. The authors also suggest an improvement by including biological component into the current model for a better representation of ecological effects.
My views:
I like the approach and totally understand the use of a single index for hydrological alterations for reducing complexity of the model. Though I would suggest some alternative approaches like developing a pareto front and evaluate scenarios for different objects, trade-off analysis. I would also like to see a weighting introduced in the IHAs so as to recognize which IHAs have more effect on the downstream ecology.
This paper is about implementing a quantitative assessment framework for determining the instream flow under multi-objective water allocation criteria using a the Range of Variability Approach (RVA) to evaluate hydrologic alterations caused by flow diversions. The resulting degrees of alterations for the 32 Indicators of Hydrologic Alterations (IHAs) are integrated into one overall degree of Hydrologic Alteration. The inclusion of this index in the objective function to optimize a water allocation scheme to minimize hydrologic alterations and water supply shortages using compromise programming is suggested.
The proposed methodology is applied to a case study of the Kaoping diversion weir in Taiwan that is designed to simultaneously assure the water supply reliability and sustain natural flow variability. The Kaoping Creek in southwestern Tainwan is 171 km long and has the largest drainage area(3,257 km2) on the island, the average annual runoff being about 8.5 billion m3. The creek supplies major proportions of the total water demand in this region. The Kaoping diversion weir with a design diversion capacity of 35 m3/s was completed in 1999, built to supply for the increasing municipal demands. The Kaoping Creek provides habitats for some endemic species and it is believed that agricultural withdrawals and municipal diversions both can effect the aquatic biota considerably dowstream of the Kaoping weir. Currently a minimum instream flow of 9.5 m3/s is being released at the weir but a minimum flow is unable to provide sufficient flow variation which is recognosed as a primary driving force for sustaining the integrity of aquatic ecosystems.
In RVA analysis, a range of variation for each IHA is determined from the prediversion flows. In this study the target range for each IHA was bracketed between 25th and 75th percentile values as suggested by Richter et al. (1998). The weir operations are aimed to make post diversion flow conditions reach the established RVA ranges at the same frequency as that of the prediversion flows.
This is a multi-objective decision making problem which involves the minimizing of the hydrologic impacts and water supply shortages as the operational goals for the Kaoping weir. The objective function can be expressed as a function of shortage ratio of the registered agriculural withdrawals, shortage ratio of the projected diversion for municipal supplies and the combined index for Hydrological Alterations whose definitions are provided in the article. All these can be expressed as the function of the instream flow value as decision variable.
The compromise programming algorithm is adopted as the authors believe its suited for the discrete problem and is still felixible for the preferences of the decision makers concerning the relative importance of each goal considered. Compromise programming identifies the optimal solution as the one that has the shortest distance to an ideal point where the multiple objectives simulatneously reach their minimum values. The ideal point is practically inachievable but may be used as a base point.The objective function involves the use of the base point and the worst point wrt each goal. It also involves the use of weights in order to decide the preferred goals.
The results indicate that the current realease of 9.5 m3/s as a minimum instream flow does not effectively restore the natural flow variations. Increasing the amount of instream flow release would reduce the overall degree of hydrologic alteration; however, this is achieved at the cost of increasing the water supply shortage ratios. An equal weighting to both water supply reliability and natural flow variability would suggest a minimum flow of 26 m3/s which is supported by the authors. The authors also suggest an improvement by including biological component into the current model for a better representation of ecological effects.
My views:
I like the approach and totally understand the use of a single index for hydrological alterations for reducing complexity of the model. Though I would suggest some alternative approaches like developing a pareto front and evaluate scenarios for different objects, trade-off analysis. I would also like to see a weighting introduced in the IHAs so as to recognize which IHAs have more effect on the downstream ecology.
Saturday, April 4, 2009
Assignment #6
This is a review of the article "Optimization of Regional Storm-Water Management Systems" by Behera et.al. in the ASCE Journal of Water Resources Planning and Management in April, 1999.
In this paper Behera et al. discuss the use of an optimization based methodology for determining the lowest cost Stormwater Management (SWM) scheme to abate stormwater quantity and quality related issues. The optimization methodology is described for obtaining design parameters like storage volume, release rate and pond depth for a SWM pond and a dynamic programming approach is discussed to extend to a multiple parallel catchment system (each with a single detention pond).
The authors say, "The natural storage capacity of urban catchments lost through the development process is offset by engineered storage facilities in the form of different types of detention ponds, which are often considered as one of various best management practices (BMPs) for storm-water control. They are implemented for peak flow attenuation, runoff volume control, and runoff quality control. Common practice is to design these facilities such
that the release from the facility maintains the pre-development runoff conditions or satisfies other local environmental regulations for runoff quantity and quality control." For the land developers the construction of SWM ponds is a loss of developable expensive land in addition to the cost of construction and O&M for these ponds. The main objective would be to optimize the costs of construction and O&M without violating relevent environmental regulations on discgarges and stormwater quality. A computational example of the proposed procedure is provided by the optimization of a system of three parallel catchments.
My thoughts:
I like the concept of using a stochastic measure for the run-off and quality control but I think this method will be more effective if we play with the release rates and look at a temporal variation on the control measure.
In this paper Behera et al. discuss the use of an optimization based methodology for determining the lowest cost Stormwater Management (SWM) scheme to abate stormwater quantity and quality related issues. The optimization methodology is described for obtaining design parameters like storage volume, release rate and pond depth for a SWM pond and a dynamic programming approach is discussed to extend to a multiple parallel catchment system (each with a single detention pond).
The authors say, "The natural storage capacity of urban catchments lost through the development process is offset by engineered storage facilities in the form of different types of detention ponds, which are often considered as one of various best management practices (BMPs) for storm-water control. They are implemented for peak flow attenuation, runoff volume control, and runoff quality control. Common practice is to design these facilities such
that the release from the facility maintains the pre-development runoff conditions or satisfies other local environmental regulations for runoff quantity and quality control." For the land developers the construction of SWM ponds is a loss of developable expensive land in addition to the cost of construction and O&M for these ponds. The main objective would be to optimize the costs of construction and O&M without violating relevent environmental regulations on discgarges and stormwater quality. A computational example of the proposed procedure is provided by the optimization of a system of three parallel catchments.
My thoughts:
I like the concept of using a stochastic measure for the run-off and quality control but I think this method will be more effective if we play with the release rates and look at a temporal variation on the control measure.
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